Tanning process



i atezniteril @ept. 19, 1922.

FATENT LORENZO DUFOUR AND GUSTAVO DUFOUR, OF GENOA, ITALY.

TANNING PROCESS.

N0 Drawing.

Application filed March 28, 1921. Serial no. 456,198.

(GRANTED UNDER THE PROVISIONS OF THE ACT OF MARCH 3, 1921, 41 STAT. In,1313.) I

To all whom it may concern:

Be it known that we; Lorenzo DUroUR and Giis'invo DUroUn, both subjectsof the King of Italy, and residents of Genoa, in the Kingdom of Italy,have invented certain new and useful Improvements in Tanning Processes(for which applications for patent have been filed as follows: in ItalyApril 6, 1918, Patent No. 165,824, dated July 18, 1919; France, filedJanuary 31, 1919, Ser. No. 108,210; Spain, filed February 17, 1919; andGreat Britain, filed Mlarch 1, 1919, No. 5,124); and we do herebydeclare the following to be a full, clear, and exact description of theinvention, such as will enable others skilled in the art to which itappertains to make and use the same.

It is well known that sulphurous an hydride (sulphur dioxide) and itssalts have a very useful effect as energetic reducing agents and aretherefore very eflicacious in preventing the oxidation of tanningliquors and consequently keeping those liquors clear, with the avoidanceof loss of tanning matters.

That beneficial action is all the more nec essary when the tanning isdone in open vessels, with the result that the tanning liquors are moreexposed to oxidation and become muddy.

Although the above mentioned action of sulphurous anhydride in thetanning of skins has been known for a long time past, as is said above,there is no evidence that sulphurous anhydride has been employed in. thegaseous state; and its use in that state forms the subject of thepresentinvention. As a matter of fact, up to the present, sulphurousanhydride has been used for the treatment of tanning extracts and ofskins, in the form of bisulphite of soda, with the object both ofdecolorizing the extract and of preparing the skins for tanning.

The new system that forms the subject of this application, and withwhich very good results are obtained, consists in the direct use ofsulphurous gas (S0 produced by the combustion of sulphur or by any othermethod of preparation. The gas is caused to enter the water in the vatsin which the skins are suspended, the liquid in those vats beingmaintained in rapid circulation, in the known manner. Otherwise the gasis introduced into and released in the water in the tubs, by a tubefollowing the axial line of the tubs.

In order to prepare the skins for tanning and to eliminate the limecompletely, instead of employing organic acids or mineral acids, whichare difficult to use and which are very often injurious to the skins,the hides are suspended in vats containing water at a temperature of 30to 35 degrees C. The water is caused to circulate rapidly and there isintroduced into it by means of an air compressor a current of sulphurousgas produced in a furnace in which sulphur is burned.

At the same time one may add to those vats some tanning liquors, takenfrom the excess in the tanningvats in order to utilize those liquorsfully at the same time as the lime is eliminated from the skins. In thatway we secure a complete utilization of the tanning extract and apartial renewal of the tanning liquor, and also make room for furtherquantities of tanning extracts in the tan vats.

After a certain time, when the skins have absorbed the tanning solutionand show-no trace of lime on the inside, they are taken out andsuspended in the tanning vats which contain a concentrated tanningsolution. In those vats the liquor is made to circulate rapidly andsulphurous anhydride is introduced from time to time, the temperaturebeing maintained at 35 degrees C. It is of advantage to have atemperature of 30-35 degrees 0., but the operation can be carried onwith liquors at ordinary temperature.

When the tanning is done in tubs one proceeds in a similar fashion,introducing the sulphurous gases through a tube opening at the bottom ofthe liquor contained in the cleaning tub or the tanning tub.

In all cases the current of sulphurous gas (S0 is kept in action untilthe water will not absorb any more of the gas and the smell of itbecomes perceptible.

The advantages of this process are as follows:

1. The lime is eliminated from the skins in a perfect way and at thesame time the tanning liquors are fully utilized.

2. A moderate plumping or swelling of and protect them from oxidation.

the skins is produced, and likewise a very fine rain.

3. lhe tanning liquors are protected from oxidation and are kept alwaysclear and limpid, one of the defects at present being that the tanningliquors used gradually turn duller and become almost muddy. ,Thusleather of very fine colour and perfectly tanned is obtained. 1

4:. The composition of the tanning liquors do not alter while theygenerally do when bisulphite of soda is added to clarify them Thebisulphite of soda becomes oxidized and converted into sulphate of soda,which accumulates in the tanning liquors, giving rise to an excessivequantity of soluble non-tanning matters, with a consequent increase ofthe percentage of ash in the tanned product.

What we claim is: p p 1. A process oftanmng which comprises.

.first cleaningthe hides in a solution im-

